Method and device for communication on a network

ABSTRACT

The communication method of the invention applies to communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in “base station” mode and the stations not supplying a control signal then functioning in “mobile station” mode. 
     The method of the invention includes, for at least one communication between two communication stations functioning in mobile station mode, in connection with a first base station:
         an operation of determining a second station, during which a communication station functioning in mobile station mode able to function in base station mode is determined,   a switching request operation during which a message representing a request to switch into base station mode is sent to the second station determined during the determination operation.

This application is a division of application Ser. No. 09/357,813, filedJul. 20, 1999 (allowed) now U.S. Pat. No. 6,894,992.

The present invention concerns a method and device for communicating ona network. It applies in particular to local wireless networks withcentralised architecture, for which each communication is organisedbetween a so-called base communication station, also referred to as the“fixed part”, and a mobile communication station, also referred to asthe “portable part”.

An example of such a communication network is given by the telephonesusing the European DECT standard (initials of the English words “DigitalEnhanced Cordless Telecommunication”).

In such a local network, a base station supplies a synchronisationsignal to all the mobile stations in the network. The set of stations(the base station and one or more mobile stations) which thussynchronise themselves with each other, constitutes a cell.

The communication capacity of a cell is fixed by the DECT standard. Whenthis capacity becomes too low, it is known that a base station can beadded, manually, so that a second cell is added to the first. However,in this case, the stations in different cells cannot communication witheach other and the cells are fixed.

According to the DECT standard, a cell cannot automatically break itselfdown into several cells in order to increase the total communicationcapacity of all the stations.

When two mobile stations have to communicate with each other, they musteach communicate with a base station, which doubles the passbandrequirement for the communication concerned.

The present invention sets out to remedy these drawbacks.

To this end, the present invention aims to allow the automatic breakdownof a cell into several cells by providing, on the one hand, that atleast one mobile station is capable of functioning as a base station andon the other hand providing mechanisms enabling the initial base stationto control the constitution of the new cell.

Thus, according to a first aspect, the present invention relates to amethod of communication between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a control signal, said station then functioning in“base station” mode and the stations not supplying a control signal thenfunctioning in “mobile station” mode, characterised in that it includes,for at least one communication between two communication stationsfunctioning in mobile station mode, in connection with a first basestation:

-   -   an operation of determining a second station, during which a        communication station functioning in mobile station mode able to        function in base station mode is determined,    -   a switching request operation during which a message        representing a request to switch into base station mode is sent        to the second station determined during the determination        operation.

By virtue of these provisions, for the communication, a new base stationwill be sought. It should be noted here that the new base station can beone of the stations which is to communicate or a third station which hasthe capability of functioning as a base station.

According to particular characteristics, the second communicationstation performs, following reception of said message:

-   -   an operation of determining agreement, or not, to function in        base station mode, and    -   an operation of replying to the base station, during which the        communication station transmits a message representing        agreement, or not, to function in base station mode.

By virtue of these provisions, the communication station envisaged asthe future base station can itself determine whether it accepts thisrole. Thus, when the initial base station is too partially or badlyinformed of the actual capability of the second communication station ofoperating in base station mode for the communication, an error can beavoided since it is the best informed communication station, the onewhich is intended to be the future base station, which finally decides.

According to particular characteristics, when at least one of thecommunication stations intended to communicate with each other iscapable of functioning in base station mode, during the operation ofdetermining the second station, one of the communication stationsintended to communicate with each other and capable of functioning inbase station mode is determined as the second station.

By virtue of these provisions, the cell can consist solely of twostations which are to communicate with each other, which simplifies thefunctioning of the network and makes it possible for the entire passbandof the new cell to serve, without having to duplicate the transmittedinformation, as is the case when a communication between two mobilestations passes through a base station.

According to particular characteristics, when, following the switchingrequest operation, the second station has switched into base stationmode, said second station performs an operation of switching into mobilestation mode, when the communication is terminated.

By virtue of these provisions, as soon as the communication isterminated, the cell in which this communication took place merges intothe cell from which it came. Different mobile stations can then onceagain communicate with each other.

According to particular characteristics, when the passband necessary fora communication between two communication stations functioning in mobilestation mode in connection with a first base station is greater than apredetermined value, there are performed, for said communication:

-   -   the operation of determining a second station, and    -   the switching request operation.

According to other particular characteristics, when the passbandnecessary for a communication between two communication stationsfunctioning in mobile station mode in connection with a first basestation is not available for the first base station, there areperformed, for said communication:

-   -   the operation of determining a second station, and    -   the switching request operation.

By virtue of each of these provisions, the decision to create a new cellis dependant upon a passband criterion and resolves any passband problemwhich could arise for the communication itself or for a futurecommunication request.

According to a second aspect, the present invention relates to a devicefor communication between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a control signal, said station then functioning in “basestation” mode and the stations not supplying a control signal thenfunctioning in “mobile station” mode, characterised in that it has aprocessing means adapted, for at least one communication between twocommunication stations functioning in mobile station mode, in connectionwith a first base station:

-   -   to determine a second communication station functioning in        mobile station mode able to function in base station mode, and    -   to send, to the second station, a message requesting switching        into base station mode.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterised in that theyhave a device as briefly disclosed above.

The invention also relates to:

-   -   a means of storing information which can be read by a computer        or a microprocessor storing instructions of a computer program        characterised in that it implements the method of the invention        as briefly disclosed above, and    -   a means of storing information which is removable, partially or        totally, and which can be read by a computer or a microprocessor        storing instructions of a computer program characterised in that        it implements the method of the invention as briefly disclosed        above.

The preferential or particular characteristics, and the advantages, ofsaid device, said computer, said camera, said facsimile machine, saidphotographic apparatus, said television receiver, said printer, saidscanner, said audio/video player and said information storage meansbeing identical to those of the method as briefly disclosed above, theseadvantages are not repeated here.

When a station has the capability of behaving either as a base stationor as a mobile station, this capability remains an exclusive item ofinformation of said communication station, which prevents its use by thenetwork.

The present invention sets out to remedy these drawbacks.

To this end, the present invention relates, according to a third aspect,to a method of communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a control signal, said station then functioning in“base station” mode and the stations not supplying a control signalfunctioning in “mobile station” mode, characterised in that it includes,performed by at least one communication station capable of functioningaccording to each of the modes, base station and mobile station, and ofswitch between these two functioning modes:

-   -   an operation of determining the presence of a station        functioning in base station mode, and    -   when, during the presence determination operation, it is        determined that a station is functioning in base station mode,        an operation of putting into communication with said base        station and an operation of transmitting, to said base station,        an item of information representing a capability of switching        from one operating mode to another.

Thus the information concerning the capability of the mobile stations ina cell to become a base station can be used by a base station for:

-   -   requesting such a mobile station to become a base station, when        the covering base station is going to become inactive,    -   requesting such a mobile station to become a secondary base        station in order to assist the initial base station to guarantee        all the necessary communications internal to the cell.

More generally, the invention makes it possible to dynamically modifythe configuration of the network and of its cell or cells.

According to particular characteristics, during the transmissionoperation:

-   -   said item of information represents a capability of switching        automatically between the two communication modes,    -   said information represents a capability of switching manually        between the two communication modes,    -   said information includes an item of information representing a        message specific to the initial proprietor of the communication        system,    -   said information includes an item of information representing a        memory capacity of said station,    -   said information includes an item of information representing a        degree of filling of the memory of said station,    -   said information includes an item of information representing a        processing capacity of a microprocessor of said station, and/or    -   said information includes an item of information representing a        maximum data rate.

By virtue of each of these provisions, the knowledge of the capabilityof the communication station which supplies this information is precise.

According to a fourth aspect, the present invention relates to a devicefor communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a control signal, said station then functioning in “basestation” mode and the stations not supplying a control station thenfunctioning in “mobile station” mode, characterised in that it has aprocessing means adapted:

-   -   to function according to each of the modes, base station and        mobile station,    -   to switch between these two functioning modes,    -   to determine the possible presence of a station functioning in        mobile station mode, and    -   when it has determined that a station is functioning in base        station mode, to get into communication with said base station        and to transmit to it an item of information representing a        capability of switching from one functioning mode to another.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterised in that theyhave a device as briefly disclosed above.

The invention also relates to:

-   -   a means of storing information which can be read by a computer        or a microprocessor storing instructions of a computer program        characterised in that it implements the method of the invention        as briefly disclosed above, and    -   a means of storing information which is removable, partially or        totally, and which can be read by a computer or a microprocessor        storing instructions of a computer program characterised in that        it implements the method of the invention as briefly disclosed        above.

The preferential or particular characteristics, and the advantages, ofsaid device, said computer, said camera, said facsimile machine, saidphotographic apparatus, said television receiver, said printer, saidscanner, said audio/video player and said information storage meansbeing identical to those of the method as briefly disclosed above, theseadvantages are not repeated here.

In a local wireless network with centralised architecture, for exampleof the type using the DECT standard, a base station can be switched offor switched automatically into mobile station mode, and a mobile stationhaving the capability of becoming a base station may have to requestgoing into base station mode in place of the current base station.

The document U.S. Pat. No. 5,691,980 discloses how a master node of anetwork can detect an excessively low battery level and choose a newmaster node amongst slave nodes. It chooses the slave node having thebest battery level. According to this document, it is the initial masternode which determines its replacement. This document does not make itpossible to take into account a system comprising heterogeneous portableterminals, as in a DECT network. In addition, according to thisdocument, a slave node cannot take the initiative in becoming a masternode.

The present invention sets out to remedy these drawbacks.

To this end, the present invention relates, according a fifth aspect, toa method of communicating between communication stations adapted tocommunicate with each other when at least one of said communicationstations supplies a control signal, said station then functioning in“base station” mode, and the stations not supplying a control signalthen functioning in “mobile station” mode, characterised in that itincludes:

-   -   a request operation during which a first communication station        transmits to a second communication station a message        representing a request to change station functioning in base        station mode.

By virtue of these provisions, a communication station functioning as abase station or a communication station functioning at a mobile stationcan require a change in organisation of the cell in order to improve itsfunctioning or in order themselves to change functioning mode. Thenetwork can thus be reconfigured dynamically, taking into accountvarious constraints, and optimise its functioning.

According to particular characteristics, during said request operation,the change request message includes an item of information representingthe identity of a mobile station envisaged as a new base station.

By virtue of these provisions, the first station which requires thechange in base station can determine and transmit the identity of thestation envisaged as the new base station.

According to particular characteristics, the first communication stationis the communication station functioning in base station mode, prior tothe request operation.

According to other particular characteristics, the second communicationstation is a communication station envisaged for functioning in basestation mode following a request operation.

By virtue of these provisions, the two partners in the communication arethe two communication stations which envisage exchanging their role inthe cell. This simplifies communication and avoids interfering with theother communication stations.

According to particular characteristics, the request operation isperformed by the communication station functioning in base station modeprior to the request operation and the second communication stationperforms, following the reception of the message representing a requestto change station functioning in base station mode:

-   -   an operation of determining agreement, or not, to function in        base station mode, and    -   an operation of response to the base station, during which the        second communication station transmits a message representing        the agreement or not to function in base station mode.

By virtue of these provisions, it is the station envisaged as the futurebase station which determines whether or not it accepts this role. Thus,if the initial base station is only partially informed of the actualcapability of the mobile station of taking the role of base station, itcannot impose this change in role on the second communication station.

According to particular characteristics, when a communication stationoperating in base station mode is switched off, it performs said requestoperation.

By virtue of these provisions, the communication station which isoperating in base station mode causes another communication station tostart to function in base station mode before stopping its ownfunctioning.

According to particular characteristics, the first communication stationis a communication station envisaged for functioning in base stationmode following the request operation.

According to other particular characteristics, the second communicationstation is the communication station functioning in base station modeprior to the request operation.

By virtue of these provisions, the two partners in the communication arethe two communication stations which envisage exchanging their role inthe cell. This simplifies communication and avoids interfering with theother communication stations.

According to particular characteristics, in the absence of a response onthe part of a second communication station, the first station considersthat the envisaged change in base station has failed.

By virtue of these provisions, the method of the invention functionsboth with devices according to the present invention and with devicesknown in the state of the art prior to the present invention.

According to particular characteristics, following the requestoperation, performed by the first communication station:

-   -   an operation of determining acceptance of change in station        functioning in base station mode, and    -   when it is determined that the envisaged change is not accepted,        a new request operation during which a new message representing        a request to change base station is addressed to another        communication station.

By virtue of these provisions, the station which requires a change inbase station may make several successive attempts to achieve thisobjective.

According to particular characteristics, each request operation includesan operation of selecting the station for which there is intended themessage requesting a change in station functioning in base station mode.

According to other particular characteristics:

-   -   the selection operation includes an operation of reading a        destination station identity in a list of communication        stations,    -   the selection operation includes an operation of determining the        mobile station having better capabilities of becoming the new        base station, and/or    -   the selection operation includes an operation of determining a        mobile station having a need to transmit.

By virtue of each of these provisions, the stations which are envisagedfor functioning in base station mode can, in a preferential order whichdepends on the characteristics of the selection operation, be thedestination of messages representing a request to change stationfunctioning in base station mode.

According to particular characteristics, the communication method asbriefly disclosed above includes, performed by a communication stationoperating in mobile station mode:

-   -   an operation of determining capability of functioning in base        station mode, and    -   said request operation, during which said request message        represents the capability of the first station of functioning in        base station mode.

By virtue of these provisions, a communication station which operates inmobile station functioning mode can determine that it is effective forit to take the role of a base station.

According to particular characteristics, on reception of said requestmessage, the second station performs:

-   -   an operation of comparing capability of functioning in base        station mode, during which it determines whether or not the        first station has a better capability than the second station of        functioning in base station mode, and,    -   in the affirmative, an operation of transmitting, to the first        communication station, a message representing an acceptance of        change in communication station functioning in base station        mode.

By virtue of these provisions, the second communication stationdetermines whether it accepts the change in base station requested.

According to a sixth aspect, the present invention relates to a devicefor communicating between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a control signal, said station then functioning in “basestation” mode and the station not supplying a control signal thenfunctioning in “mobile station” mode, characterised in that it has, in afirst communication station, a processing means adapted to transmit, toa second communication station, a request message representing a requestto change station functioning in base station mode.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterised in that theyhave a device as briefly disclosed above.

The invention also relates to:

-   -   a means of storing information which can be read by a computer        or a microprocessor storing instructions of a computer program        characterised in that it implements the method of the invention        as briefly disclosed above, and    -   a means of storing information which is removable, partially or        totally, and which can be read by a computer or a microprocessor        storing instructions of a computer program characterised in that        it implements the method of the invention as briefly disclosed        above.

The preferential or particular characteristics, and the advantages, ofsaid device, said computer, said camera, said facsimile machine, saidphotographic apparatus, said television receiver, said printer, saidscanner, said audio/video player and said information storage meansbeing identical to those of the method as briefly disclosed above, theseadvantages are not repeated here.

The document U.S. Pat. No. 5,691,980 discloses how a master node in thenetwork can detect an excessively low battery level and choose a newmaster node amongst slave nodes. It chooses the slave node having thebest battery level. According to this document, it is the initial masternode which determines its replacement. This document does not make itpossible to take into account a system comprising heterogeneous portableterminals, as in a DECT network. In addition, according to thisdocument, a slave node cannot take the initiative in becoming a masternode.

When the base station is no longer in a position to correctly fulfilthis role or when the quality of the transmission is not sufficient, noprior art is known which allows automatic switching of a mobile stationinto a base station.

To this end, according to a seventh aspect, the present inventionrelates to a method of communication between communication stationsadapted to communicate with each other when at least one of saidcommunication stations supplies a control signal, said station thenfunctioning in “base station” mode and the stations not supplying acontrol signal then functioning in “mobile station” mode, characterisedin that it includes, performed by a station functioning in base stationmode:

-   -   an operation of determining the capability of said station        functioning in base station mode of continuing this role, and    -   when, during the capability determination operation, it is        determined that said capability is reduced, a request operation        during which a first communication station transmits, to a        second communication station, a message representing a request        to change station functioning in base station mode.

By virtue of these provisions, the cell can reconfigure itselfautomatically when the base station leaves the cell or when a mobilestation which could have better capabilities of functioning as a basestation than a current base station enters the cell.

According to particular characteristics, during said request operation,the change request message includes an item of information representingthe identity of a mobile station envisaged as a new base station.

By virtue of these provisions, the first station, which requires thechange of base station, can determine and transmit the identity of thestation envisaged as a new base station.

According to particular characteristics, the first communication stationis the communication station functioning in base station mode, prior tothe request operation.

According to other particular characteristics, the second communicationstation is a communication station envisaged for functioning in basestation mode following the request operation.

By virtue of these provisions, the two partners in the communication arethe two communication stations which envisage exchanging their role inthe cell. This simplifies communication and avoids disturbing the othercommunication stations.

According to particular characteristics, the request operation isperformed by the communication station functioning in base station modeprior to the request operation and the second communication stationperforms, following the reception of the message representing a requestto change station functioning in base station mode:

-   -   an operation of determining agreement, or not, to function in        base station mode, and    -   an operation of response to the base station, during which the        second communication station transmits a message representing        the agreement or not to function in base station mode.

By virtue of these provisions, it is the station envisaged as the futurebase station which determines whether or not it accepts this role. Thus,if the initial base station is only partially informed of the actualcapability of the mobile station of taking the role of base station, itcannot impose this change in role on the second communication station.

According to particular characteristics, the communication stationoperating in base station mode determines said capability as a functionof the quantity of energy which it has available.

According to other particular characteristics, said communicationstation functioning in base station mode performs an operation switchinginto mobile station mode when the quantity of energy which it hasavailable is less than a predetermined value.

By virtue of these provisions it reduces its energy consumption bychanging from a base station functioning mode, which entails a highenergy consumption, to a mobile station functioning mode for which theenergy is principally consumed during communication.

According to other particular characteristics, the communication stationoperating in base station mode determines said capability according tothe quality of transmission between it and mobile stations.

By virtue of these provisions, when the initial base station moves awayfrom the other communication stations in the cell, and more generallywhen it no longer provides sufficient transmission quality, anothercommunication station is called onto take the role of base station.

-   -   According to particular characteristics, the first communication        station is the communication station functioning prior to the        base station mode request operation.

According to other particular characteristics, the second communicationstation is a communication station envisaged for functioning in basestation mode following the request operation.

By virtue of these provisions, the two partners in the communication arethe two communication stations which envisage exchanging their role inthe cell. This simplifies communication and avoids disturbing the othercommunication station.

According to particular characteristics, in the absence of a response onthe part of a second communication station, the first station considersthat the envisaged change in base station has failed.

By virtue of these provisions, the method of the invention functionsboth with devices according to the present invention and with devicesknown in the state of the art prior to the present invention.

According to particular characteristics, following the requestoperation, performed by the first communication station:

-   -   an operation of determining acceptance of change in station        functioning in base station mode, and

when it is determined that the envisaged change is not accepted, a newrequest operation during which a new message representing a request tochange base station is addressed to another communication station.

By virtue of these provisions, the station which requires a change inbase station can make several successive attempts to achieve thisobjective.

According to particular characteristics, each request operation includesan operation of selecting a station for which there is intended themessage requesting a change in station functioning in base station mode.

According to other particular characteristics:

-   -   the selection operation includes an operation of reading a        destination station identity from a list of communication        stations,    -   the selection operation includes an operation of determining the        mobile station having better capabilities of becoming the new        base station,    -   the selection operation includes an operation of determining a        mobile station having a requirement to transmit,    -   the selection operation includes an operation of determining a        mobile station which has already operated in base station mode.

By virtue of each of these provisions, the stations which are envisagedfor functioning in base station mode can, in a preferential order whichdepends on the characteristics of the selection operation, bedestinations for the messages representing a request to change stationfunctioning in base station mode.

According to an eighth aspect, the present invention relates to a devicefor communication between communication stations adapted to communicatewith each other when at least one of said communication stationssupplies a control signal, said station then functioning in “basestation” mode and the stations not supplying a control signal thenfunctioning in “mobile station” mode, characterised in that it has aprocessing means adapted:

-   -   to determine the capability of a communication station        functioning in base station mode of continuing this role, and    -   when it has determined that the said capability is reduced, to        cause a first communication station to transmit to a second        communication station a message representing a request to change        station functioning in base station mode.

The invention also relates to a network, a computer, a camera, afacsimile machine, a photographic apparatus, a television receiver, aprinter, a scanner and an audio/video player, characterised in that theyhave a device as briefly disclosed above.

The invention also relates to:

-   -   an information storage means which can be read by a computer or        a microprocessor storing instructions of a computer program        characterised in that it implements the method of the invention        as briefly disclosed above, and    -   an information storage means which is partially or totally        removable and can be read by a computer or microprocessor        storing instructions of a computer program characterised in that        it implements the method of the invention as briefly disclosed        above.

Other advantages, aims and characteristics of the present invention willemerge from the following description, given with reference to theaccompanying drawings, in which:

FIG. 1 depicts, schematically, an operating flow diagram of a mobilestation, with a view to its insertion in a network, in accordance withthe prior art,

FIG. 2 depicts schematically a network including communication devicesaccording to the second, fourth, sixth and eighth aspects of the presentinvention, adapted to implement the communication method of the first,third, fifth and seventh aspects of the present invention,

FIG. 3A depicts schematically the architecture of an electronic circuitincorporated in a communication device according to the second, fourthand sixth aspects of the present invention,

FIG. 3B depicts schematically the architecture of an electronic circuitincorporated in a communication device according to the eighth aspect ofthe present invention,

FIG. 4 depicts schematically an operating flow diagram of acommunication device according to the second, fourth, sixth and eighthaspects of the present invention, with a view to its insertion in anetwork,

FIG. 5 details part of the flow diagram illustrated in FIG. 4,

FIG. 6A depicts schematically the organisation of information sent by acommunication device according to the second, fourth and sixth aspectsof the present invention, with a view to informing a base station of thecapabilities of this device related to functioning in base station mode,

FIG. 6B depicts schematically the organisation of information sent by acommunication device according to the eighth aspect of the presentinvention, with a view to informing a base station of the capabilitiesof this device related to functioning in base station mode,

FIGS. 7, 8A and 8B depict schematically exchanges of informationoccurring between communication devices according to the second, fourth,sixth and eighth aspects of the present invention, when a mobile stationjoins or leaves a cell,

FIGS. 9, 10, 11 and 12 depict schematically operating flow diagrams ofcommunication devices according to the second, fourth, sixth and eighthaspects of the present invention, with a view to a change in basestation,

FIG. 13 is a schematic time representation of the messages exchangedbetween communication devices in accordance with the flow diagrams inFIGS. 9 to 12,

FIGS. 14A and 14B depict schematically the organisation of informationsent by communication devices according to the second, fourth, sixth andeighth aspects of the present invention, with a view to collectinginformation concerning the capability of mobile stations of functioningin base station mode,

FIGS. 15 and 16 depict schematically messages exchanged betweencommunication devices according to the second, fourth, sixth and eighthaspects of the present invention, with a view to collecting informationconcerning the capability of mobile stations of functioning in basestation mode,

FIG. 17 depicts schematically a physical frame structure known in thestate of the art,

FIG. 18A depicts schematically a communication internal to a cellaccording to the state of the art,

FIGS. 18B and 18C depict schematically a cell split implemented by thedevice which is the object of the second, fourth, sixth and eighthaspects of the present invention,

FIGS. 19 and 20 depict schematically operating flow diagrams ofcommunication devices according to the second, fourth, sixth and eighthaspects of the present invention, with a view to splitting the cellduring an internal communication,

FIGS. 21A, 21B and 22 depict schematically information exchangesoccurring between communication devices according to the second, fourth,sixth and eighth aspects of the present invention, with a view tosplitting the cell during an internal communication,

FIG. 23 depicts schematically a flow diagram of classification of mobilestations as a function of criteria defining their capability offunctioning as a base station,

FIG. 24 depicts schematically a flow diagram implemented by acommunication station functioning initially as a mobile station, with aview to communication, in the absence of a base station,

FIG. 25 depicts schematically a flow diagram implemented by acommunication station functioning initially as a mobile station, onreception of a message requesting a change in base station in accordancewith the message illustrated in FIG. 6B,

FIG. 26 depicts schematically a flow diagram implemented by acommunication station connected to an external network,

FIG. 27 depicts schematically a flow diagram implemented by acommunication station functioning initially as a base station, when itscapability of pursuing this functioning mode decreases,

FIG. 28 depicts schematically a flow diagram implemented by acommunication station functioning initially in mobile station mode, onreception of a message requesting a change in base station,

FIG. 29 depicts schematically a flow diagram implemented by acommunication station, functioning in base station mode, in order todetermine a radio transmission quality, and

FIG. 30 depicts schematically a flow diagram implemented by acommunication station functioning initially in mobile station mode, buthaving already functioned in base station mode, when its capabilities offunctioning in base station mode have been restored.

In the description which follows, the term “communication device”designates a communication station able to behave, in a communicationnetwork, as a base station or as a mobile station, in accordance on theone hand with the DECT standard and on the other hand with the differentfunctioning modes described in relation to the accompanying drawings.

FIG. 1 describes the procedure of locking a mobile station onto a signaltransmitted by a base station, as known in the prior art.

When a mobile station is powered up, it goes into an internalinitialisation state 101. Next, during an operation 102, the mobilestation goes into reception mode on the next channel (there are ten ofthem) in the frequency band allocated for communications in accordancewith the DECT standard (that is to say 1880 to 1900 MHz), seeking asignal transmitted by a base station which is suitable to it. Whenoperation 102 is first iterated, it is the first channel which ischosen. When, before performing operation 102, the last channel isconsidered, it is the first channel which is chosen, during operation102.

Next, during a test 103, the mobile station listens out on the radiochannel under consideration, for a predetermined period, in order todetect a synchronisation pulse coming from a base station. The mobilestation thus determines whether or not a base station is using thechannel under consideration for sending a synchronisation signal.

When the result of test 103 is negative, during a test 104, the mobilestation determines whether or not the channel under consideration is thelast one. When the result of test 104 is negative, operation 102 isreiterated. When the result of test 104 is positive, during an operation105, the mobile station goes into standby mode and then, during anoperation 107, it waits for a predetermined period T0 (which can be adecreasing function of the energy resources of the mobile station),before reiterating operation 102.

When the result of test 103 is positive, during a test 108, the mobilestation determines whether or not it has a right of access to the basestation which sends the synchronisation signal.

To this end, when the result of test 103 is positive, the mobile stationcan obtain the information broadcast by the base station, everymulti-frame (each multi-frame being composed of sixteen frames with aduration of ten milliseconds). Amongst the information broadcast by thebase station, there is notably the so-called “ARI” parameter (initialsof the words “Access Rights Identity”) which defines the access rightsto the base station under consideration. Each mobile station having atleast one identity referred to as “PARK” (initials of the words“Portable Access Rights Key”), it is the correspondence between at leastone of the “PARK” identities and the “ARI” parameter which is testedduring test 108.

When the result of test 108 is negative, test 104 is performed. When theresult of test 108 is positive, during an operation 109, the mobilestation locks onto the base station which is sending the synchronisationsignal detected on the channel under consideration.

At the end of operation 109, the mobile station can obtain theinformation broadcast by the base station whose ARI parametercorresponds with at least one of its “PARK” identities.

The mobile station can then initiate or accept a connection by means ofthe base station onto which the mobile station is locked. The mobilestation can then communicate with the other mobile stations which arealso locked onto the same base station and with the base station itself,in particular when the latter supplies an access point to anothernetwork, for example by telephone.

It should be noted here that, if there is no base station which issending a synchronisation signal, no communication is possible betweenthe mobile stations, in accordance with the prior art.

FIG. 2 depicts, in one and the same local area 200, differentcommunication devices in accordance with the present invention:

-   -   the communication devices 202 and 203 are telephones of a known        type, complying, for example, with the DECT GAP standard        (initials of the words “Generic Access Profile”) and which is        dedicated to portable telephone voice transmission,    -   the communication devices 201, 204 and 205 are multimedia        terminals able to behave, in the cell 200, as a base station or        as a mobile station.

In the embodiment described and depicted, the communication devices 201,204 and 205 support the DECT GAP standard, and comply with the type “A”data profile, relating to data transfers up to a rate of 24 kilobits persecond. The communication device 201 also complies with the type “AB”data profile, relating to the transfer of data up to a rate of 552kilobits per second, but can switch into base station mode onlyfollowing a manual operation by the user.

Each device according to the present invention, 201, 204 and 205,operates, by default, in accordance with the description of FIG. 1, thatis to say, at the time of initialisation, it goes into mobile stationfunctioning mode.

In FIG. 3A, it can be seen that each communication device according tothe second, fourth and sixth aspects of the present invention, 201, 204or 205, has, connected together by a bus 301:

-   -   a controller 306,    -   a DECT base band unit 302,    -   a DECT radio unit 303, itself connected in addition to a        sending/receiving antenna 307,    -   a random access memory 304,    -   a read-only memory 305,    -   a keyboard 307,    -   a display 308,    -   an energy level controller 309, itself connected in addition to        an electrical power supply 310 (battery, accumulator or mains),        and    -   an input/output interface 311.

The controllers 306 and 309 and the DECT base band unit 302 consist infact of a processor and an operating program stored in the read-onlymemory 305.

The DECT base band unit 302 is of a known type and is adapted to exploitall the capabilities of the DECT standard known up to the time of thepresent invention.

The controller 306 is adapted to implement the method of the inventionand in particular the flow diagrams illustrated in the figures. Theenergy level controller 309 is intended to evaluate the available energylevel, in a known fashion, in order to determine timing values (seebelow).

The random access memory 304 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

-   -   temporary variables l and k,    -   a variable “MO” representing the current operating mode, mobile        station or base station,    -   a variable “MD” representing the random access memory.        available,    -   a variable “CMD” representing a value coefficient for the        available memory which takes one of three values “0”, “1” or “2”        depending on whether the memory area available has a capacity        less than two predetermined values MD_N1 and MD_N2, is between        the two predetermined values or is greater than the two        predetermined values,    -   a memory area “Tx/Rx” reserved for the reception or transmission        of data,    -   a table “Table_SM” containing a list of the identities of the        mobile stations (including the devices according to the present        invention) declared to the base station, and the information        associated with these mobile stations,    -   list “List_SM_auto” containing a list of the identities of the        devices according to the present invention, that is to say those        able to change operational mode automatically (for example        stations 204 and 205),    -   a list “List_SM_manual” containing a list of the identities of        the mobile stations able to change operational mode, through the        intervention of their user (for example station 201), and    -   a list “List_SM_direct” containing a list of the identities of        the mobile stations able to communicate directly with each        other, without a base station.

The read-only memory 305 stores, in registers which, for convenience,each bear the same name as the data which they contain:

-   -   an item of information “CM” on the memory capacity of the        device,    -   an item of information “CP” on the capacity of the processor of        the device,    -   an indicator “IP” representing profiles of the DECT standard        supported by the device (in fact by its DECT base band unit        302),    -   an item of information “TS” representing the types of time        intervals (referred to as “slots” in the remainder of the        description and, in particular, in FIG. 17, a term in accordance        with the usage of persons skilled in the art of communications)        which are DECT supported (single, double or half-slot),    -   an item of information “DM” representing a maximum data rate        supported by the device (for example between 24 and 552 kilobits        per second),    -   the memory area capacity values MD_N1 and MD_N2,    -   an item of information representing its identity,    -   a coefficient “CPR” representing the number of DECT profiles        supported,    -   an item of information “CO” representing the operational        capability of the device. This information can take the        following values:    -   “SB”: the device can operate only in base station mode,    -   “SM”: the device can operate only in mobile station mode,    -   “SB/SM_manual”: the device can change operating mode through the        intervention of its user,    -   “SB/SM_auto”: the device can automatically change operating        mode,    -   “SM/SM_direct”: the device can communicate directly with another        mobile whose information “CO” takes the value “SM/SM_direct”,        and    -   an item of information “BA” representing the automatic or manual        switching capability from a base station functioning mode to a        mobile station functioning mode and vice versa (“BA” being equal        to “true”, when this capability exists, and “false” otherwise).

The read-only memory 305 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterised in that it implementsthe method of the invention. According to a variant, the read-onlymemory 305 is removable, partially or totally, and has for example amagnetic strip, a flash memory, a diskette or a fixed-memory compactdisc (CD-ROM).

In FIG. 3B, it can be seen that each communication device according tothe eighth aspect of the present invention, 201, 204 or 205, has,connected together by a bus 301:

-   -   a controller 306,    -   a DECT base band unit 302,    -   a radio unit 303, itself connected in addition to a        sending/receiving antenna 307,    -   a random access memory 304,    -   a read-only memory 305,    -   a keyboard 307,    -   a display 308,    -   an energy level controller 309, itself connected in addition to        an electrical power supply 310 (battery, accumulator or mains),    -   an input/output interface 311, and    -   a communication quality controller 312.

The controllers 306 and 309 and the DECT base band unit 302 consist infact of a processor and an operating program stored in the read-onlymemory 305.

The DECT base band unit 302 is of a known type and is adapted to exploitall the capabilities of the DECT standard known up to the time of thepresent invention.

The controller 306 is adapted to implement the method of the inventionand, in particular, the flow diagrams illustrated in the figures. Theenergy level controller 309 is intended:

-   -   to recognise the type of electrical power supply (mains or        battery), in a known fashion, and to evaluate the energy level        available for the communication device, in order to determine:    -   time delay values (see below), and    -   an ability to become a base station or to remain so.

The communication quality controller 312 is adapted to evaluate thequality of the radio signal and to supply a value QR representing thisquality.

The random access memory 304 stores, in registers which, forconvenience, each bear the same name as the data which they contain:

-   -   temporary variables l and k,    -   a value “QR” representing the quality of the radio signal        measured by the controller 312,    -   a value “NB” representing an available energy quantity,    -   a value “DB” representing the past functioning of the station,        in base station mode,    -   a variable “MO” representing the current operating mode, mobile        station or base station,    -   a variable “MD” representing the random access memory available,    -   a variable “CMD” representing a value coefficient for the        available memory which takes one of three values “0”, “1” or “2”        depending on whether the memory area available has a capability        less than two predetermined values MD_N1 and MD_N2, is between        the two predetermined values or is greater than the two        predetermined values,    -   a memory area “Tx/Rx” reserved for the reception or transmission        of data,    -   a table “Table_SM” containing a list of the identities of the        mobile stations (including the devices according to the present        invention) declared to the base station, and the information        associated with these mobile stations,    -   a list “List_SM_auto” containing a list of the identities of the        devices according to the present invention, that is to say those        able to change operational mode automatically (for example        stations 204 and 205),    -   a list “List_SM manual” containing a list of the identities of        the mobile stations able to change operational mode, through the        intervention of their user (for example station 201), and    -   a list “List_SM_direct” containing a list of the identities of        the mobile stations able to communicate directly with each        other, without a base station.

The read-only memory 305 stores, in registers which, for convenience,each bear the same name as the data which they contain:

-   -   an item of information “CM” on the memory capacity, of the        device,    -   an item of information “CP” on the capacity of the processor of        the device,    -   a minimum communication quality value QR_min,    -   a maximum communication quality value QR_max,    -   a minimum available energy quantity value NB_min,    -   a maximum available energy quantity value NB_max,    -   an indicator “IP” representing the profiles of the DECT standard        supported by the device (in fact by its DECT base band unit        302),    -   an energy coefficient “CE” which represents the energy source of        the station under consideration, according to three values:        “CE_HIGH”, equal to “2”, for a printer, copier, facsimile        machine or office computer, and more generally for any equipment        which is generally connected to the mains or which has a means        of detecting connection to the mains which indicates that the        station is connected to the mains, “CE_MID”, equal to “1”, for a        portable computer and more generally for a communication station        which can operate either on the mains or on a battery, and        “CE_LOW”, equal to “0”, for a pocket organiser or portable        telephone, and more generally for a communication station which        operates almost exclusively on a battery,    -   a fixity coefficient “CF” which represents the normal mobility        of the station under consideration, according to three values:        “CF_HIGH”, equal to “2”, for a printer, copier, facsimile        machine or office computer, and more generally for any equipment        which generally fixed, “CF_MID”, equal to “1”, for a portable        computer and more generally for a communication station which        can be moved but which is generally not in movement during its        operation, and “CF_LOW”, equal to “0”, for a pocket organiser or        portable telephone, and more generally for a communication        station which may be in movement during its use,    -   an item of network interface information “IR” which represents        the types of network which can be accessed by the station, equal        to “0” when no other network can be accessed and being non-nil        when another network can be accessed, the positions of the bits        equalling “1” in the binary representation of “IR” indicating        which types of network can be accessed:    -   xxxx xxx1 PSTN (Public Switched Telephone Network)    -   xxxx xx1x ISDN (Integrated Service Digital Network)    -   xxxx x1xx LAN (Local Area Network)    -   xxxx 1xxx ATM (Asynchronous Transfer Mode),    -   a network interface coefficient “CIR” which represents the        number of external networks accessible,    -   an item of information “TS” representing the types of time        intervals (referred to as “slots” in the remainder of the        description and, in particular, in FIG. 17, a term in accordance        with the usage of persons skilled in the art of communications)        which are DECT supported (single, double or half-slot),    -   an item of information “DM” representing a maximum data rate        supported by the device (for example between 24 and 552 kilobits        per second),    -   the memory area capacity values MD_N1 and MD_N2,    -   an item of information representing its identity,    -   a coefficient “CPR” representing the number of DECT profiles        supported,    -   an item of information “CO” representing the operational        capability of the device. This information can take the        following values:    -   “SB”: the device can operate only in base station mode,    -   “SM”: the device can operate only in mobile station mode,    -   “SB/SM manual”: the device can change operating mode through the        intervention of its user,    -   “SB/SM_auto”: the device can automatically change operating        mode,    -   “SM/SM_direct”: the device can communicate directly with another        mobile whose information “CO” takes the value “SM/SM_direct”,        and    -   an item of information “BA” representing the automatic or manual        switching capability from a base station functioning mode to a        mobile station functioning mode and vice versa (“BA” being equal        to “true”, when this capability exists, and “false” otherwise).

The read-only memory 305 constitutes a means of storing informationwhich can be read by a computer or a microprocessor, storinginstructions of a computer program characterised in that it implementsthe method of the invention. According to a variant, the read-onlymemory 305 is removable, partially or totally, and has for example amagnetic strip, a flash memory, a diskette or a fixed-memory compactdisc (CD-ROM).

The procedure followed by the controller 306 for determining theoperating mode (base station or mobile station) is detailed in FIG. 4.When a communication device according to the present invention ispowered up, it goes into an internal initialisation state 401. Next,during an operation 402, the communication device goes into receptionmode on the next channel of the frequency band allocated forcommunications in accordance with the DECT standard, as disclosed withregard to operation 102 (FIG. 1).

Next, during a test 403, the communication device listens to the radiochannel under consideration, for a predetermined period, in order todetect a synchronisation pulse coming from a base station (including thecase of another communication device behaving as a base station). Thecommunication device thus determines whether or not a base station isusing the channel under consideration for sending a synchronisationsignal.

When the result of test 403 is negative, during a test 404, thecommunication device determines whether or not the channel underconsideration is the last. When the result of test 404 is negative,operation 402 is reiterated.

When the result of test 403 is positive, during a test 405, thecommunication device determines whether or not it has a right of accessto the base station which is sending the synchronisation signal, asdescribed with regard to operation 108 (FIG. 1).

When the result of test 405 is negative, the communication deviceperforms test 404. When the result of test 405 is positive, during anoperation 406, identical to operation 109 (FIG. 1), the communicationdevice locks onto the base station which is sending the synchronisationsignal detected on the channel under consideration.

At the end of operation 406, the communication device can obtain theinformation broadcast by the base station whose ARI parametercorresponds with at least one of its “PARK” identities. Thecommunication device can also initiate or accept a connection by meansof the base station onto which the device is locked. The communicationdevice can then communicate on the one hand with the other mobilestations and the communication devices according to the presentinvention which behave as a mobile station, and which are also lockedonto the same base station, and on the other hand with the base stationitself or with the communication device which is behaving as a basestation.

When the result of test 404 is positive, during an operation 407, thecontroller 306 of the communication device causes this communicationdevice to switch into base station mode.

In this base station functioning mode, it sends, at regular time slots,with a duration less than the predetermined duration of test 403, asynchronisation signal, on one of the DECT channels. The duration of theregular time slot is, according to the DECT standard, 160 milliseconds.

Next, the communication device allows a time T1 to pass (for example oneminute), operation 408, whilst continuing its functioning as a basestation, before performing a test 409, during which it determineswhether mobile stations are synchronised with it (see detail of test 409in FIG. 5).

When the result of test 409 is negative, during an operation 411, thecontroller 306 causes the functioning mode to switch into mobile stationmode, and then the communication device allows a predetermined time T2to pass (for example as a decreasing function of the available energyevaluated by the energy level controller 309), operation 412, beforerenewing operation 402.

When the result of test 409 is positive, during an operation 413, thecommunication device allows a predetermined time T3 to pass (for exampleas an increasing function of the available energy evaluated by theenergy level controller 309), whilst continuing its functioning in basestation mode, before performing a test 414, during which thecommunication device determines whether or not at least onecommunication with a mobile station is active. When the result of test414 is positive, it is reiterated. When the result of test 414 isnegative, during an operation 415, the controller 306 causes thecommunication device to switch from base station mode to mobile stationmode. Next, the communication device reiterates operation 402.

It will be understood that, in accordance with the flow diagram of FIG.4, two operating criteria are used:

-   -   when, in mobile station functioning mode, the communication        device detects no base station, it goes into base station        functioning mode, and    -   when, in base station functioning mode, the communication device        detects no mobile station, it goes into mobile station        functioning mode.

In addition, when, in base station functioning mode, the communicationdevice does not detect any communication with a mobile station, it goesinto mobile station functioning mode. The purpose of the latterarrangements is to cause the base station to return to mobile stationmode before once again seeking whether another base station can bedetected.

In order to detect the presence of mobile stations (including the caseof communication devices according to the present invention which behaveas a mobile station), the case is chosen, with regard to FIG. 5, inwhich each communication device able to function in base station mode isinformed of the identity of each communication device and of each mobilestation able to communicate with it.

In this case, the communication device first of all performs a test 501(FIG. 5), during which the controller 306 determines whether or not thelist of mobile stations able to communicate with the communicationdevice is empty. When the result of test 501 is positive, the result oftest 409 is negative, operation 502. When the result of test 501 isnegative, during an operation 503, a temporary variable l, which servesas an indicator on said list, is initialised to the value “0”. Then,during an operation 504, the communication device sends, to the network,a message requesting an answer to the device identified by the l^(th)identifier of the list. Then the communication device allows apredetermined time T4 to pass, operation 505, before performing a test506, during which it determines whether or not an answer message hasbeen sent by a communication device. When the result of test 506 ispositive, during a test 507, the device determines whether the identityof the device which sent the answer message corresponds to the identityof the device which was called during operation 504. When the result oftest 507 is positive, the result of test 409 is positive, operation 510.When the result of test 507 is negative, or when the result of test 506is negative, during an operation 508, the value of the variable l isincremented.

Next, during a test 509, the communication device determines whether ornot the value of the variable l is less than or equal to the size of thelist. When the result of test 509 is positive, operation 504 isreiterated. When the result of test 509 is negative, the result of test409 is negative, operation 502.

As a variant, in order to detect the presence of mobile stations, thefollowing procedure is used: when a mobile station detects a basestation and locks onto this base station, the mobile station sends tothe base station a message representing its identity and itscapabilities (see below). The base station can then update a list ofmobiles present in the cell. Conversely, when a mobile station leavesthe cell (that is to say the area of coverage of the base station) orbefore switching off, it sends to the base station a message indicatingthat it is terminating its access rights.

It should be noted here that the procedure of detecting that a mobilestation is leaving its cell is known from the prior art, by analysingthe signal reception power.

FIG. 6A depicts the structure of information concerning the operationalmode capability of a station in the network, according to the first tosixth aspects of the present invention. This information can betransmitted in DECT protocol messages using a field reserved for thetransfer of non-standardised information, referred to in the standard as“escape-to-proprietary”. According to the invention, thenon-standardised information is used solely in the following messages inthe standard:

-   -   “access-fights-request”, and    -   “locate-request”, which includes an attachment request.

The first octet 601 of the field described in FIG. 6A indicates that theinformation elements which follow are non-standardised information to besent within a DECT protocol message. The second octet 602 contains theinformation octet number to be transmitted. The third octet 603indicates that the octets 604 and 605 contain an EMC (“EquipmentManufacturer Code”) parameter, which serves to identify the manufacturerusing this proprietary information. Thus, if an item of equipment whoseEMC parameter is different from that indicated by the octets 604 and605, it does not process the information which follows.

Naturally, if the present invention were to be the subject ofstandardisation between different manufacturers, octets 601, 604 and 605would no longer be used in the same way.

Octet 606 represents the operational capability CO (identical to itsvalue, in the embodiment described and depicted) of the device whichacts as a mobile station. The following octets, 607 to 611, whose numberis equal to the number of information octets to be transmitted (numberrepresented by octet 602) minus four, serve to transmit more preciseinformation on the capabilities of the device of operating as a basestation. For example, the following parameters can be transmitted:

-   -   memory capacity of the device (octet 607),    -   degree of filling of the memory of the device (octet 608),    -   power, speed of the processor of the device (octet 609), and    -   maximum rate supported by the device (octet 610),

The position bit 8 (on the left) of the information octets 607 to 610takes one of the values:

-   -   “1”, when the information element is transmitted in this        message, or    -   “0” when the value of the following bits of the octet has no        meaning (the information element is not transmitted in the        message).

FIG. 6B depicts the structure of information concerning the operationalmode capability of a station in the network, according to the seventhand eighth aspects of the present invention. This information can betransmitted in DECT protocol messages using a field reserved for thetransfer of non-standardised information, referred to in the standard as“escape-to-proprietary”. According to the invention, thenon-standardised information is used solely in the following messages inthe standard:

-   -   “access-rights-request”, and    -   “locate-request”, which means “request for location” and which        includes an attachment request.

The first octet 701 of the field described in FIG. 6B indicates that theinformation elements which follow are non-standardised information to besent within a DECT protocol message. The second octet 702 contains theinformation octet number to be transmitted. The third octet 703indicates that the octets 704 and 705 contain an EMC (“EquipmentManufacturer Code”) parameter, which serves to identify the manufacturerusing this proprietary information. Thus, if an item of equipment whoseEMC parameter is different from that indicated by the octets 704 and705, it does not process the information which follows.

Naturally, if the present invention were to be the subject ofstandardisation between different manufacturers, octets 701, 704 and 705would no longer be used in the same way.

Octet 706 represents the operational capability CO (identical to itsvalue, in the embodiment described and depicted) of the device whichacts as a mobile station. The following octets, 707 to 711, whose numberis equal to the number of information octets to be transmitted (numberrepresented by octet 702) minus four, serve to transmit more preciseinformation on the capabilities of the device for operating as a basestation. For example, the following parameters can be transmitted:

-   -   memory capacity of the device (octet 707),    -   degree of filling of the memory of the device (octet 708),    -   power, speed of the processor of the device (octet 709), and    -   maximum rate supported by the device (octet 710),    -   fixity coefficient “CF” (octet 712),    -   energy coefficient “CE” (octet 713),    -   network interface “IR” (octet 714).

The position bit 8 (on the left) of the information octets 707 to 710takes one of the values:

-   -   “1”, when the information element is transmitted in this        message, or    -   “0” when the value of the following bits of the octet has no        meaning (the information element is not transmitted in the        message).

FIG. 7 describes how a mobile station obtains rights of access to a basestation and how it terminates its rights of access. The access rightsprocedure enables a base station and a mobile station to exchange theirrespective identities and information concerning the capabilities of themobile station. The mobile station initiates the procedure by sending,to the base station, a message “access_rights_request” which containsnotably the capabilities of the mobile station in the field “terminalcapability”. In this field, according to the invention, use is made ofthe profile indicator parameter (“profile indicator”) and slot typeparameter (“slot type capability”) (see below).

The additional information necessary for the functioning of the deviceaccording to the present invention is transmitted in the field “escapeto proprietary” of the message “access_rights_request” (FIGS. 6A and6B).

When a base station receives a message “access_rights_request” if themobile station is authorised to access the resources of the basestation, the latter returns a message “access_rights_accept”, and adds,in the table of the declared mobile stations, the information concerningthe mobile station which sent the message “access_rights_request”

According to the first to sixth aspects of the present invention, theinformation thus collected is stored in the table_SM, of the randomaccess memory 304, organised in the following fashion:

No Identity CO CM RM CP IP TS DM . . .

1

2

. . .

When a mobile station is added to the table_SM, the followinginformation concerning it are stored therein:

-   -   its mobile identity,    -   its operational capability (CO),    -   its memory capacity (CM),    -   the degree of filling of its memory (RM),    -   its processor capacity (CP),    -   its profile indicator (IP),    -   its slot type capability (TS),    -   its maximum throughput (DM), and possibly other information        characterising it.

The parameters IP and TS are read in the field “Terminal Capability” ofthe message “access_rights_request”, whilst the parameters CO, CM, RM,CP and DM are read in the field “escape to proprietary” described inFIG. 6A. When a mobile station wishes to terminate its access rights toa base station, it sends a message 803“access_rights_terminate_request”. The base station then erases theinformation concerning this mobile station in its table_SM and returns amessage “access_rights_terminate_accept” 804. The mobile station canthen no longer use the resources of the base station.

According to the seventh and eighth aspects of the present invention,the information thus collected is stored in the table_SM, of the randomaccess memory 304, organised in the following fashion:

No Identity CO CM RM CP IP TS DM CE CF IR

1

2

. . .

When a mobile station is added to the table_SM, the followinginformation concerning it are stored therein:

-   -   its mobile identity,    -   its operational capability (CO),    -   its memory capacity (CM),    -   the degree of filling of its memory (RM),    -   its processor capacity (CP),    -   its profile indicator (IP),    -   its slot type capability (TS),    -   its maximum throughput (DM),    -   its energy coefficient (CE),    -   its fixity coefficient (CF),    -   its network interface information (IR),

and, optionally, other information characterising it.

The parameters IP and TS are read in the field “Terminal Capability” ofthe message “access_rights_request”, whilst the parameters CO, CM, RM,CP, DM, CF, CE and IR are read in the field “escape to proprietary”described in FIG. 6B. When a mobile station wishes to terminate itsaccess rights to a base station, it sends a message 803“access_rights_terminate_request”. The base station then erases theinformation concerning this mobile station in its table_SM and returns amessage “access_rights_terminate_accept” 804. The mobile station canthen no longer use the resources of the base station.

FIG. 8A illustrates how a mobile station attaches itself to or detachesitself from a base station. When a mobile station enters the cell of abase station over which the mobile station has obtained access rights,it must initiate a procedure of attachment to the base station. By thisprocedure, the mobile station indicates to the base station that it isready to receive calls. To attach itself, the mobile station sends tothe base station a message “Locate_request” 811 which containsinformation concerning notably the identity and capabilities of thecommunication station and the possibility of sending non-standardisedinformation. With the message “Locate_request” 811, it is possible totransfer to the base station the same information as with the message“access_rights_request”. If a mobile station has important changes toits parameters (for example memory space still available) compared withthe time of the access right procedure, it can use the field “escape toproprietary” as defined in FIGS. 6A and 6B, to inform the base stationthereof.

When a base station receives a message “Locate_request” 811, it verifiesthat the mobile station is identified in its “table_SM” and, in theaffirmative, returns a message “Locate_accept” 812. The base stationthen uses the information contained in its “table_SM”, the table of thedeclared mobile stations, in order to insert the mobile station underconsideration in the appropriate list, List_SM_auto, if its operationalcapability CO is equal to SB/SM_auto, List_SM_manual if its operationalcapability CO is equal to SB/SM_manual or List_SM direct if itsoperational capability is equal to SM/SM_direct.

The reverse procedure to attachment is detachment. When a mobile stationleaves the cell or is switched off, it sends a message “detach” 813 tothe base station, which then withdraws the mobile station from the listcorresponding to its operational capability.

However, the detachment procedure may not always be initiated by themobile station which leaves the cell (because of breakdown or excessivespeed for example). The last part, in FIG. 8B, illustrates how the basestation can periodically check on the validity of the information whichit is keeping in the list stored in its random access memory 304.

The base station then periodically sends a request for a procedure ofupdating its location (or its attachment), by means of a message“MM_info_suggest” 821, whose field “info_type” is equal to“locate_suggest”. The procedure of updating the location of a mobilestation is identical to the attachment procedure, the messages 822 and823 being respectively identical to the messages 811 and 812.

By virtue of the provisions illustrated in FIGS. 7, 8A and 8B, the listlist_SM_auto contains all the mobile stations present in the cell andhaving the capability of switching automatically between base stationmode and mobile station mode.

As explained with regard to FIG. 23, the list_SM_auto is classifiedaccording to the decreasing capability of the mobile stations ofbecoming a base station: the first element in the list concerns themobile station which has the best capability of becoming a base station.In order to classify this list, after each attachment, detachment orupdating procedure, the base station takes into account all theparameters stored in the table_SM_auto (CM, RM, CP, IP, TS, DM, . . .according to the first to sixth aspects of the invention; CM, RM, CP,IP, TS, DM, CF, CE, IR, . . . according to the seventh and eighthaspects of the invention).

The list₁₃ SM_manual is sorted in the same way as the list_SM_auto.These lists can be used in the following situations:

-   -   the base station becomes inactive following a powering down or a        switching into mobile station mode and it seeks a replacement        base station amongst the mobile stations having a capability of        becoming a base station, the base station is excessively used        (memory full, number of simultaneous communications greater than        a predetermined value) and it seeks a second base station for        taking over some of the traffic.

The base station then chooses the first mobile station in thelist_SM_auto. If the list_SM_auto is empty, or if none of the stationsin the list list_SM_auto is suitable, the base station can have recourseto the first mobile station represented in the list_SM_manual. It mustthen transmit a message which triggers the display or sending of asignal to the mobile station chosen in order to warn the user that achange of functioning mode at the mobile station under consideration isrequired.

The base station uses the list_SM_direct so that the communicationsinternal to the cell each involving at least one station represented inthis list are directly organised by this station.

FIGS. 9 and 10 illustrate how a base station in activity (referred to as“initial”) finds a replacement base station (referred to as “final”),for example when the initial base station can no longer fulfil its roleas base station (switching off or automatic or manual switching tomobile station mode).

The procedure described in FIG. 9 can be implemented only when there isno active connection. In addition, any new connection request is refusedduring this procedure.

As illustrated in FIG. 9, the initial base station commences with a test902 during which it determines whether or not another base station ispresent (as illustrated in FIG. 1). When the result of the test 902 ispositive, the procedure is complete, with success, since the mobilestations which communicate with the initial base station will be able toreplace the latter for their communications and the initial base stationchanges functioning mode and becomes a mobile station, operation 912.

When the result of test 902 is negative, during a test 903, the initialbase station determines whether or not the list_SM_auto is empty. Whenthe result of test 903 is positive, the procedure is ended, havingfailed, since no mobile station can take the role of base station. Theuser is then informed that, if the base station ceases its activity, allthe communications will be suspended, operation 913.

When the result of test 903 is negative, during an operation 904, thevariable l is initialised to the value. “0”. Then, during an operation905, the initial base station sends a message “new_base_request” to thel^(th) mobile station in the list_SM_auto. During operation 905, theinitial base station waits for a sufficient period of time to enable amobile station in accordance with the device which is the object of thepresent invention to reply, before performing a test 906. Next, duringthis test 906, the initial base station determines whether or not it hasreceived, from the mobile station under consideration, a message“new_base_accept”.

When the result of test 906 is positive, during an operation 907, theinformation stored in the table table_SM, and in the lists list_SM_auto,list_SM_manual and list_SM_direct, are transferred into the randomaccess memory of the mobile station under consideration. Next, during atest 908, the initial base station determines whether or not it hasreceived, from the mobile station under consideration, a data transferacknowledgement message. When the result of test 908 is negative, it isreiterated. When the result of test 908 is positive, the initial basestation changes operating mode, operation 912, and the base stationchange operation is ended, on the initial base station side, withsuccess.

When the result of test 906 is negative, the initial base stationconsiders that the allocation of the base station role has been refusedby the l^(th) station in the list list_SM_auto. Then, during anoperation 910, the value of the variable l is incremented by 1. Then,during a test 911, the initial base station determines whether or notthe value of the variable l is greater than or equal to the number ofmobile stations represented in the list_SM_auto.

When the result of test 911 is negative, operation 905 is reiterated.When the result of test 911 is positive, the base station changeprocedure is ended, having failed, and the user is warned that thecessation of the activity of the initial base station will cause thesuspension of all the communications, operation 913.

According to a variant, not shown, when, during test 911, it isdetermined that the list list_SM_auto has been entirely run through, theoperations and tests 905 to 912 are reiterated, running through the listlist_SM_manual. Operation 912 is then performed only after the mobilestation which sent the message “new-base-accept” (test 906) has sent amessage confirming change in functioning mode.

When the procedure has been ended with success, by the detection ofanother base station during test 902 or by the acknowledgement of aninformation transfer by a mobile station during a test 908, the basestation has thus changed operating mode and has become a mobile station,unless the procedure illustrated in FIG. 9 has been brought about by aswitching off of the initial base station, in which case the latterceases its activity.

FIG. 10 illustrates the procedure of changing base station on the partof a mobile station, when, during a test 1001, it determines that amessage “new_base_request” has been received from the base station andis intended for the mobile station under consideration. Next, during atest 1002, the mobile station determines whether or not its operatingcapability CO has one of the values SB/SM_auto or SB/SM_manual,determining whether or not the value of the information “BA” is “true”.When the result of test 1002 is negative, during an operation 1004, amessage “new_base_reject” is sent by the mobile station underconsideration to the base station in order to indicate to it that theallocation of the base station role has been refused. Then the procedureis ended, without the mobile station having switched into base stationfunctioning mode.

When the result of test 1002 is positive, during a test 1003, the mobilestation determines whether its available memory capacity MD is strictlyless than the value MD_N1 stored in the read-only memory 305. This valueMD_N1 corresponds in fact to a minimum available memory capacity fortaking the base station role.

When the result of test 1003 is positive, operation 1004 is performed.When the result of test 1003 is negative, during an operation 1005, themobile station sends a message accepting the role of base station“new_base_accept”, to the initial base station. Then, during a test1006, the mobile station determines whether it has received, from theinitial base station, the necessary information for taking the basestation role, that is to say all the information stored in the listslist_SM_auto, list_SM_manual and list_SM_direct, and in the tabletable_SM.

When the result of test 1006 is negative, it is reiterated. When theresult of test 1006 is positive, during an operation 1007, the mobilestation sends, to the base station, an acknowledgement of receipt of theinformation. Then, during an operation 1008, the mobile station changesfunctioning mode and becomes a base station. The procedure is thenended.

Where the mobile station has an operating code value SB/SM_manual, thetest 1003 is supplemented by:

-   -   a triggering of a warning signal intended to warn the user that        he must manually switch the operating mode of the communication        station concerned,    -   a wait for a sufficient period for the user to have the time to        effect the manual switching, and    -   a test of change of operating mode by the user (not shown) and,        where the user has not effected the change in operating mode        during a predetermined period which follows the test 1003,        operation 1004 is performed.

It will be noted that, in accordance with the functioning modeillustrated in FIGS. 9 and 10, the initial base station uses staticcriteria, that is to say which do not immediately change value accordingto the change in the network or mobile stations, in order to choose areplacement base station, whilst the mobile station envisaged as thefuture base station can accept or refuse the role of new base station,using dynamic criteria, that is to say taking into account immediatelyany change in the state of the mobile station which would prevent itsactivity as a base station.

FIGS. 11 and 12 illustrate how, at the initiative of a station which isinitially a mobile station, a change in base station can be effected.For example, when such a mobile station has locked onto the initial basestation, following its being powered up, and when this mobile station isa candidate for being a base station (for example because it supportsall the variants and the most extensive modes of the DECT standard), atest 1101 is positive. Otherwise, this procedure is ended. When theresult of test 1101 is positive, during an operation 1102, the mobilestation listens to the channel known, in the DECT standard, under thename of “Q”. On this channel, in fact, the initial base stationregularly broadcasts information which may be useful to mobile stationsand, in particular, information concerning the DECT profiles which itsupports.

Next, during a test 1103, the mobile station determines whether or notit has better capabilities of being a base station than the initial basestation. When the result of test 1103 is negative, the procedure isended. When the result of test 1103 is positive, during an operation1104, the mobile station sends a message “chg_base_request”, which meanschange in base required, to the initial base station, and then allows asufficient period to pass for the base station to be able, if it is inaccordance with the communication device of the present invention, tosend a message in answer.

Then, during a test 1105, the mobile station determines whether or notit has received, in return, from the base station, a message“chg_base_accept”, which means acceptance of change in base. When theresult of test 1105 is negative, the mobile station considers that ithas received a refusal to change base on the part of the initial basestation, and the base change procedure is ended.

When the result of test 1105 is positive, the operations 1106, 1107 and1108 are respectively identical to operations 1006, 1007 and 1008. Thenthe base station change procedure is ended.

On the initial base station side, when, during a test 1201, itdetermines that it has received a message “chg_base_request”, from amobile station which is locked, it performs a test 1202 during which itdetermines whether or not, both at the same time, the information “BA”representing its communication capability is equal to “true” and itsoperating mode MO corresponds to that of a base station.

When the result of test 1202 is negative, during an operation 1203, theinitial base station sends, to the mobile station under consideration, amessage “chg_base_reject”. Then the procedure is ended. When the resultof test 1202 is positive, during an operation 1204, the initial basestation sends, to the mobile station under consideration, a message“chg_base_accept”. Then, during a test 1205, the initial base stationdetermines whether or not there is an active connection.

When the result of test 1205 is positive, it is reiterated. When theresult of test 1205 is negative, during an operation 1206, the basestation sends, to the mobile station under consideration, theinformation stored in the table table_SM, and in the lists list_SM_auto,list_SM_manual and list_SM_direct.

Next, during a test 1207, the initial base station determines whether ornot it has received, from the mobile station under consideration, amessage acknowledging the data transfer. When the result of test 1207 isnegative, it is reiterated. When the result of test 1207 is positive,during an operation 1208, the initial base station changes operatingmode and starts to function in mobile station mode, and the operation ofchanging base station is ended with success.

FIG. 13 depicts:

-   -   in the form of messages 1301 to 1304, the messages exchanged        between the initial base station, on the left, and the mobile        station which will become a base station, on the right, in the        context of the procedure illustrated in FIGS. 9 and 10, and    -   in the form of messages 1305 and 1306, the messages exchanged        between a mobile station, on the left, and the base station, in        the context of the procedure illustrated in FIGS. 11 and 12.

In order to collect information concerning the capability of the mobilestations present in the network of operating in base station mode, thebase station according to the present invention uses a message of thebroadcast type illustrated in FIG. 14A. The base station thusinterrogates all the mobile stations in order to obtain the followinginformation:

-   -   a list of the mobile stations which can switch automatically        into base station mode,    -   this same list sorted according to one or more parameters chosen        by the base station,    -   the identity of the mobile station which has the best overall        capability of operating in base station mode, at a given        instant,    -   the identity of the mobile station which has the best capability        of operating in base station mode, according to one or more        criteria fixed by the base station.

A first type of message 1401 (in FIG. 14A) is a request from the basestation broadcast to all the mobile stations, which includes thefollowing fields:

-   -   a message code field 1402 “broadcast_SB_req”, which means        approximately “request broadcast by the base”    -   a type field 1403 CT, defining the type of request concerned,    -   a length field 1404 CL, which defines the number of parameters        in the request, and    -   parameter fields 1405 CP(0) to 1406 CP(CL-1), which contain the        criteria with respect to which the answer is awaited.

The type field 1403 CT and length field 1404 CL can take differentvalues, making it possible to specify to the different mobile stationshow to respond to the request and according to which criteria, thelatter being specified by the fields 1405 to 1406.

When the information transmitted in the field 1403 CT is equal to “0”,each mobile station must without delay send its capability of acting asa base station and, if the value contained in the field 1404 CL isnon-nil, each mobile station must return the value of the parametersspecified in the request.

When the information transmitted in the field 1403 CT is equal to “1”,each mobile station must send its capability of acting as a base stationafter a period whose value represents the value of the capability of themobile station of becoming a base station, and, if the value containedin the field 1404 CL is non-nil, each mobile station must return thevalue of the parameters specified in the request.

The measurement of the capability of the mobile station of becoming abase station is determined in accordance. with the answer time describedbelow.

According to the first to sixth aspects of the invention, the parametersrepresented by the fields 1405 to 1406 include:

-   -   the operational capability CO,    -   the available memory capacity,    -   the DECT profiles supported,    -   the DECT slot type supported (single, double or half-slot), and    -   the computing capacity of the central unit.

According to the seventh and eighth aspects of the invention, theparameters represented by the fields 1405 to 1406 include:

-   -   the operational capability CO,    -   the available memory capacity CM,    -   its energy coefficient CE,    -   its fixity coefficient CF,    -   its network interface information IR,    -   the DECT profiles supported,    -   the DECT slot type supported (single, double or half-slot), and    -   the computing capacity of the central unit.

The message 1411 “broadcast_SB_ans” (in FIG. 14B), which meansapproximately “answer to the message broadcast by the base station”concerns the answer of the different mobile stations to the basestation. This message 1411 is sent using the oriented connection mode.It includes the following fields:

-   -   a message code field 1412,    -   an identity field 1413, in which the mobile station specifies        its identity,    -   an answer field 1414 CR, stating the answer of the mobile        station,    -   a length field 1415 CL′, representing the number of data in the        answer,    -   data fields 1416 to 1417, containing the data required by the        base station.

The answer field 1414 CR can take the following values:

-   -   “accept” (“acceptance”), meaning that the communication station        has the capability of acting as a base station, the data fields,        if the field length 1415 indicates a non-nil length, then give        information concerning the parameters required by the base        station,    -   “reject” (“refusal”), meaning that, momentarily, the mobile        station cannot act as a base station or does not have        information relating to the parameters required by the base        station. The data fields, if the field length 1415 indicates a        non-nil length, can then give an explanation for the rejection.

An absence of answer to the message 1401, on the part of a mobilestation, is considered to be an answer whose answer field CR would be“reject”, when a predetermined period of time has elapsed.

By default, if in the message 1401 the operational capability is notrequired, only the mobile stations having the capability of switchingautomatically from one functioning mode to another can respond by meansof a message 1411.

FIG. 15 represents an exchange of messages between the base station andeach mobile station having the capability of becoming a base station.The message 1401 is broadcast by the base station at regular time slots,for example every minute.

In FIG. 15, the message 1401A is a message 1401 of the type withoutdelay (CT=0) and the length field CL is also equal to “0”. Each of themobile stations according to the present invention then answers byreturn (that is to say without waiting), in the form of messages 1411A,1411B or 1411C. In the example described the mobile stations 204, 205and 201 answer, the first two with an answer field CR of the “accept”type and the last with an answer field CR of the “reject” type.

In order to determine the answer field, each mobile station according tothe present invention determines whether or not its operating code isone of the codes “SB/SM_auto” or “SB/SM_manual”, and, in theaffirmative, whether its available memory capacity is greater than thepredetermined value MD_N1.

In FIG. 16, the broadcast message 1401B is a message 1401 of the typewith delay (CT=1) and with parameters (CL=1), the only parameter adoptedbeing the operational capability. The mobile stations which have acapability of functioning as a base station answer whilst waiting for aperiod of time which is a function of the value of their operationalcapability: the first mobile stations which answer have an operationalcapability equal to “SB/SM_auto” (message 1411D and 1411E), whilst thelast mobile station which responds has an operational capability equalto “SB/SM_manual” (message 1411F).

In general terms, in the embodiment of the first to sixth aspects of thepresent invention, the period of waiting before the answer is determinedas from the instant of receiving the message 1401B. This period takesthe value:T _(answer) =CCO.t _(CO) +CPR.t _(CPR) +CMD.t _(CMD),

-   -   a formula in which:    -   CCO is the operational capability coefficient (which is equal to        “0” if the operational capability is “SB/SM_auto”, “5” if the        operational capability is “SB/SM_manual”, “5” if the operational        capability is “SM/SM_direct” and infinity if the operational        capability is equal to “SM”),    -   CPR is the supported profiles coefficient (which is equal to “0”        if the profiles supported are B, MMAP and GAP; “1” if the        profiles supported are A and GAP and “2” if the only profile        supported is GAP),    -   CMD is the available memory coefficient,    -   t_(CCO) is the period allocated to the operational capability        coefficient,    -   t_(CPR) is the period allocated to the supported profile        coefficient,    -   t_(CMD) is the period allocated to the available memory        coefficient.

For example the above three periods are equal to 10 milliseconds (theperiod of a DECT frame for the answer period always to be a multiple ofthe period of a DECT frame).

In general terms, in the embodiment of the seventh and eighth aspects ofthe present invention, the period of waiting before the answer isdetermined as from the instant of receiving the message 1401B. Thisperiod takes the value:T _(answer) =CCO.t _(CO) +CPR.t _(CPR) +CND.t _(CMD) +CE.t _(CE) +CF.t_(CF) +CIR.t _(CIR),

a formula in which:

-   -   CCO is the operational capability coefficient (which is equal to        “0” if the operational capability is “SB/SM_auto”, “5” if the        operational capability is “SB/SM_manual”, “5” if the operational        capability is “SM/SM_direct” and infinity if the operational        capability is equal to “SM”),    -   CPR is the supported profiles coefficient (which is equal to “0”        if the profiles supported are B, MMAP and GAP, “1” if the        profiles supported are A and GAP and “2” if the only profile        supported is GAP),    -   CMD is the available memory coefficient,    -   t_(CCO) is the period allocated to the operational capability        coefficient,    -   t_(CPR) is the period allocated to the supported profile        coefficient,    -   t_(CMD) is the period allocated to the available memory        coefficient,    -   t_(CE) is the period allocated to the energy coefficient,    -   t_(CF) is the period allocated to the fixity coefficient,    -   t_(CIR) is the period allocated to the network interface        coefficient.

For example the above six periods are equal to 10 milliseconds (theperiod of a DECT frame for which the answer period is always a multipleof the period of a DECT frame).

In FIG. 16, the formula for calculating the answer time is limited to

-   -   T_(answer)=CCO.t_(CO),

since the only parameter represented in the message 1601 is theoperational capability parameter.

FIG. 17 shows that the messages are transmitted according to apredetermined timing. Each communication cycle 1701, 1702 or 1703 lasts10 milliseconds and is divided into twelve equal time slots. For acommunication, one or more time slots for each cycle are allocated in afixed manner.

FIG. 18A depicts the state of the art for establishing a connectioninternal to a cell. FIG. 18A shows the route of an internalcommunication between a mobile station 1802 and a mobile station 1803.This communication passes through a base station 1801. The informationwhich pass at time t over the link between the mobile station 1802 andthe base station 1801 next passes over the link between the base station1801 and the mobile station 1803. There is therefore a duplication ofthe information and a dual occupation of the communication medium of thecell for two transmissions of the same information.

This dual occupation of the communication medium is not critical whenthe information transmitted is voice information. In the case of a datacommunication, the duplication of the links, of the information and ofthe occupation of the communication medium may saturate the cell andblock a request for connection to the outside of the cell.

In FIGS. 18B and 18C, the functioning of the device which is the objectof the present invention can be seen, a functioning intended to avoidsuch a duplication.

In this functioning:

-   -   when at least one of the mobile stations which is to        communicate, referenced 1805 and 1806, is capable of functioning        in base station mode, or when the mobile stations 1805 and 1806        are both capable of communicating direct, the cell is organised        so that communication between the two mobile stations is direct,        without passing through another station,    -   and, in the contrary case, a mobile station 1810 capable of        functioning as a base station takes this role vis-á-vis the two        mobile stations 1805 and 1806 which are to communicate and        constitutes with them a new cell, in order to release the        initial base station 1804 from the traffic concerning        communication between the mobile stations 1805 and 1806.

FIG. 19 shows, in the form of a flow diagram, how the creation of a newcell is implemented or the mobile stations are put in directcommunication.

When, during an operation 1901, the base station 1804 receives a callrequest internal to the cell, from a mobile station 1806 and intendedfor a mobile station 1805, it performs a test 1902 during which itdetermines:

-   -   whether the connection requested requires a number of slots        greater than a predetermined value (for example four slots, a        value beyond which the communication is necessarily other than a        voice communication), or    -   whether the number of slots necessary is greater than the number        of slots available.

When the result of test 1902 is negative, during an operation 1903, theconnection between the mobile stations 1805 and 1806 is established bymeans of the base station, in a fashion known in the state of the artprior to the present invention.

When the result of test 1902 is positive, during a test 1904, the basestation determines whether or not at least one of the mobile stations1805 or 1806 has a current connection.

When the result of test 1904 is positive, operation 1903 is performed.When the result of test 1904 is negative, during a test 1905, the basestation determines whether or not the mobile stations 1805 and 1806 areboth in the list SM_direct. When the result of test 1905 is positive,during an operation 1906, the base station sends, to each of the mobilestations 1805 and 1806, a message “switch-mode-request” in order toindicate to them to switch into direct communication mode, and toindicate to them the identity of the mobile station which constitutestheir interlocutor (see FIG. 21B).

In the event of failure of the implementation of the directcommunication between the mobile stations 1805 and 1806 (for example ifone of the mobile stations rejects the switching into directcommunication mode), a test 1907 is performed (see below).

In the event of success in putting the mobile stations 1805 and 1806 indirect communication, at the end of their direct communication, the twomobile stations synchronise themselves once again with the base station1804.

When the result of test 1905 is negative, during a test 1907, the basestation 1804 determines whether or not the mobile station 1805 is in thelist_SM_auto. When the result of test 1907 is positive, during anoperation 1908, the base station 1804 sends to the mobile station 1805 amessage “switch-mode-request” 2101 (FIG. 21A) in order to indicate to itthat it should switch into base station mode and sends it the identityof the mobile station 1806 so that the mobile station 1805 allocatesaccess rights to it.

In addition, on reception of a message “switch-mode-accept” 2102 fromthe mobile station 1805, the base station 1804 sends to the mobilestation 1806 a message “switch-base-request” 2103 containing theidentity of the base station 1805, in order to indicate to the mobilestation 1806 that it should synchronise itself with the new base station1805 (see FIG. 21A).

In the event of failure of the switching of the mobile station 1805 intobase station mode (for example if it rejects the switching), a test 1909is performed (see below).

When the result of test 1907 is negative, during a test 1909, the basestation 1804 determines whether or not the mobile station 1806 is in thelist_SM_auto. When the result of test 1909 is positive, during anoperation 1910, the base station 1804 sends to the mobile station 1806 amessage “switch-mode-request” 2101 in order to indicate to it that itshould switch into base station mode and sends it the identity of themobile station 1805 so that the mobile station 1806 allocates accessrights to it.

In addition, on reception of a message “switch_mode_accept” 2102 fromthe mobile station 1806, the base station 1804 sends to the mobilestation 1805 a message “switch-base-request” 2103 containing theidentity of the base station 1806, in order to indicate to the mobilestation 1805 that it should synchronise itself with the new base station1806.

It will be seen, with regard to FIG. 21A, that, for the one of themobile stations which switches into base station mode, as soon as thedata communication 2104 between the stations 1805 and 1806 is ended, itreturns to mobile station mode after having sent a message“switch-base-request” 2105 to the mobile station with which it wascommunicating data. The mobile station which receives this message 2105then synchronises itself once again with the base station 1804.

In the event of failure of the switching of the mobile station 1806 intobase station mode (for example if it rejects the switching), anoperation 1911 is performed (see below).

When the result of test 1909 is negative, during an operation 1911 (FIG.20), the base station determines whether or not the number of slotswhich remain available is strictly less than the number of slotsnecessary for the requested communication.

When the result of test 1911 is negative, operation 1903 is performed.When the result of test 1911 is positive, during an operation 1912, thetemporary variable k is initialised to the value “0”. Then, during atest 1913, the base station determines whether or not the value of thevariable k is strictly less than the size of the list list_SM_auto. Whenthe result of test 1913 is negative, operation 1903 is performed. Itshould be noted here that the performance of operation 1903 does notguarantee the setting up of the communication, rejection proceduresbeing provided, in accordance with the known state of the art. When theresult of test 1913 is positive, during a test 1914, the base stationdetermines whether or not the k^(th) station in the list list_SM_autohas a current connection.

When the result of test 1914 is positive, during an operation 1915, thevalue of the variable k is incremented by 1. Then test 1913 isreiterated. When the result of test 1914 is negative, during anoperation 1916, the base station 1804 sends, to the mobile stationidentified at the k^(th) position in the list list_SM_auto, here themobile station 1810, a message “switch-mode-request”, and then, if themobile station under consideration 1810 agrees to take the role of thenew base station, the initial base station 1804 sends, to each of themobile stations 1805 and 1806, a message “switch-base-request”,indicating the identity of the new base station 1810 so that each of themobile stations 1805 and 1806 synchronises itself with the new basestation 1810 (see FIG. 22).

At the end of the communication between the mobile stations 1805 and1806, the new base station 1810 once again switches into mobile stationfunctioning mode.

If, on reception of the message “switch-mode-request”, the mobilestation 1810 refuses to change communication mode, by sending a message“switch-mode-reject”, or by not responding to the message“switch-mode-request”, operation 1915 is performed by the base station1804.

According to a variant, not shown, when the result of test 1913 isnegative, the part of the flow diagram illustrated in FIGS. 19 and 20,starting from test 1907, is once again implemented, but considering thelist “list SM_manual” in place of the list “list_SM_auto”.

In FIG. 21A it can be seen that, for the mobile station 1805 to switchinto base station mode and for the mobile station 1806 to attach itselfto the base station 1805, the initial base station 1804 sends first ofall, to the mobile station 1805, a message “switch-mode-request” 2101and awaits in return a message “switch_mode_accept” 2102. Then theinitial base station 1804 sends, to the mobile station 1806, a message“switch-base-request” 2103, and awaits in return a message“switch-base-accept” 2106.

When the communication between the stations 1805 and 1806 is ended, themessage “switch-base-request” 2105 is followed in return by a message“switch-base-accept” 2107.

In FIG. 21B it can be seen that, to establish direct communicationbetween the mobile stations 1805 and 1806, during operation 1906, thebase station 1804 first of all sends, to one of the mobile stationsinvolved in the communication to be set up (for example the station1805), a message 2111 “switch-mode-request”, indicating the requestedcommunication mode (direct communication mode) and indicating theidentity of the other mobile station. On reception of a message“switch-mode-accept” 2112 from the mobile station (station 1805 in ourexample) for which the message “switch-mode-request” 2111 was intended,the base station 1804 sends, to the other mobile station involved in thecommunication (station 1806 in our example), a message“switch-mode-request” 2113 indicating the requested communication mode(direct communication mode) and indicating the identity of the othermobile station. On reception of a message “switch-mode-accept” 2114 fromthe mobile station (station 1806 in our example) for which the message“switch-mode-request” 2113 was intended, the two mobile stations switchinto direct communication mode. At the end of the communication, thestation 1805 sends, to the station 1806, a message “switch-mode-request”2116 and receives in return a message “switch-mode-accept” 2117, and thetwo stations 1805 and 1806 then switch into mobile station mode.

In FIG. 22, it can be seen that, to establish a communication betweenthe mobile stations 1805 and 1806 by means of a new base station 1810,during operation 1916, the base station 1804 first of all sends, to themobile station 1810, a message “switch-mode-request” 2201 indicating therequired communication mode, base station mode, and the two mobilestations 1805 and 1806 to which access rights are to be opened. Onreception, from the mobile station 1810, of a message“switch-mode-accept” 2202, the base station 1804 sends, to the mobilestation 1806, a message “switch-base-request” 2203.

On reception of a message “switch-base-accept” 2208 in return, the basestation 1804 sends, to the mobile station 1805, a message“switch-base-request” 2204. Each of the messages 2203 and 2204indicates, to each of the mobile stations, that the new base stationwhich concerns them is station 1810.

After the mobile station 1805 has sent a message “switch-base-accept”2209 to the base station 1804, mobile stations 1805 and 1806 attachthemselves to the new base station 1810.

By means of communications 2205 and 2206, the mobile stations 1806 and1805 then communicate data to each other, through the new base station1810. At the end of the communication of the data, the new base station1810 sends, to the mobile station 1806, a message “switch-base-request”2207 and, to the mobile station 1805, a message “switch-base-request”2208, indicating to each of the mobile stations that the new basestation is the station 1804.

On reception, in return, of messages “switch-base-accept” 2210 and 2211,from the mobile stations 1805 and 1806, the base station 1810 switchesinto mobile station mode.

FIG. 23 describes a flow diagram for classifying mobile stations havinga capability of switching automatically into base station mode, as afunction of criteria defining this capability of becoming a basestation.

Naturally, a similar procedure can be followed to classify the list ofmobile stations having a capability of switching manually into basestation mode.

The procedure illustrated in FIG. 23 is executed by a base station whena new mobile station (hereinafter designated SMk) joins itself to a celland sends a message illustrated in FIGS. 6A and 6B.

When this event occurs, during an operation 3201, the controller 306 ofthe base station effects an initialisation of the temporary variable Ito the value “0”. Then, during a test 3202, the controller 306determines whether or not the value of the temporary variable l isgreater than or equal to the size of the list list_SM_auto. When theresult of test 3202 is positive, during an operation 3207, the identityof the mobile station SMk is inserted at position I in the listlist_SM_auto, and the classification procedure is terminated.

When the result of test 3202 is negative, during a test 3203, thecontroller 306 determines whether or not the maximum transmission rateof the station SMk is strictly greater than the maximum rate of thel^(th) station of the list list_SM_auto.

When the result of test 3203 is positive, operation 3207 is performed.When the result of test 3203 is negative, during a test 3204, thecontroller 306 determines whether or not the maximum transmission rateof the station SMk is strictly less than the maximum rate of the l^(th)station in the list list_SM_auto.

When the result of test 3204 is positive, during an operation 3208, thevalue of the temporary variable l is incremented by 1 and test 3202 isreiterated. When the result of test 3204 is negative, during a test3205, the controller 306 determines whether or not the memory capacityof the station SMk is strictly greater than the memory capacity of thel^(th) station in the list list_SM_auto.

When the result of test 3205 is positive, operation 3207 is performed.When the result of test 3205 is negative, during a test 3206, thecontroller 306 determines whether or not the memory capacity of thestation SMk is strictly less than the memory capacity of the l^(th)station in the list list_SM_auto.

When the result of test 3206 is positive, operation 3208 is performed.When the result of test 3206 is negative, a new parameter for thecapability of becoming a base station is considered and tests similar totests 3203 and 3204, or 3205 and 3206, are performed, considering thisnew parameter in place of the maximum transmission rate (tests 3203 and3204) or memory capacity (tests 3205 and 3206). Naturally, theparameters tested are tested in decreasing order of importance. When thelast parameter has been considered with once again a negative result forthe two tests concerning it, operation 3207 is performed.

It will now be described how, when a station has determined that it hasbetter capabilities of being a base station than the current station, itsends to it a message “chg-base-request”, which includes informationrepresenting its fixity coefficient CF, its energy coefficient CE andits network interface coefficient CIR.

On reception of this message the initial base station then successivelycompares these coefficients, in decreasing order of their importance(the communication coefficient is of greater importance than the fixitycoefficient, itself of greater importance than the energy coefficient):for each coefficient successively processed:

-   -   if the initial base station has a better coefficient than the        mobile station, it rejects the change in base, by means of a        message “chg-base-reject”    -   if the initial base station has a lesser coefficient than the        mobile station, it accepts the change in base, by means of a        message “chg-base-accept”, and    -   in the latter case (equality for the coefficient under        consideration) it goes to the following coefficient.

When all the coefficients have been processed, the base station returnsan acceptance of change in base, in the form of a message“chg-base-accept”.

For implementing this procedure, the mobile station follows the flowdiagram illustrated in FIG. 11, only operation 1104 being modified inorder to transmit, in the message “chg-base-request”, informationrepresenting the coefficients CF, CE and CIR.

The base station then performs the operations illustrated in FIG. 25.First of all, during an operation 2501, the base station receives amessage “chg-base-request”. Next, during a test 2502, the base stationdetermines whether or not its operating mode is the base station mode(MO=SB) and at the same time it has the capability of changingfunctioning mode (BA=true). When the result of test 2502 is negative,the controller 306 of the base station performs an operation 2505,during which it sends a message “chg-base-reject” to the mobile stationwhich sent the message “chg-base-request”. The procedure is then ended(on a failure).

When the result of test 2502 is positive, during a test 2503, thecontroller 306 determines whether or not the coefficient CIR received isnil. When the result of test 2503 is positive, during a test 2512, thecontroller 306 determines whether or not the coefficient CIR stored inthe read-only memory 305 is nil. When the result of test 2512 isnegative, operation 2505 is performed. When the result of test 2512 ispositive, during a test 2504, the controller 306 determines whether ornot the coefficient CF received is less than or equal to the coefficientCF stored in the read-only memory 305 and at the same time thecoefficient CE received is less than or equal to the coefficient CEstored in the read-only memory 305.

When the result of test 2504 is positive, operation 2505 is performed.When the result of test 2504 is negative, an operation 2507, describedbelow, is performed.

When the result of test 2503 is negative, during a test 2506, thecontroller 306 determines whether or not the coefficient CIR received isdifferent from the coefficient CIR stored in the read-only memory and atthe same time the coefficient CIR stored in the read-only memory isdifferent from “2”.

When the result of test 2506 is negative, test 2504 is performed. Whenthe result of test 2506 is positive, during operation 2507, the initialbase station sends, to the mobile station which sent the message“chg-base-request”, a message “chg-base-accept”. Next, during a test2508, the controller 306 determines whether or not the coefficient CIRstored in the read-only memory is nil.

When the result of test 2508 is negative, the procedure is completed andthe initial base station remains in base station mode. When the resultof test 2508 is positive, during a test 2509, the controller 306determines whether or not a connection is active. When the result oftest 2509 is positive, it is reiterated. When the result of test 2509 isnegative, during an operation 2510, the initial base station switchesinto mobile station mode.

Where the communication station is combined with an access to anexternal network, the device illustrated in FIG. 3B also has:

-   -   an external communication means 314 accessing an external line        315 of an external network, and    -   a line controller 313.

The line controller 313 is adapted to detect the taking of the externalline 315 by the external communication means 314.

In this case, it functions by implementing the flow diagram illustratedin FIG. 26. It will be seen there that initially such a device functionsin base station mode, operation 2601. It then performs a test 2602,during which it determines whether or not the external line is taken,using the line controller 313.

When the result of test 2602 is negative, it is reiterated. When theresult of test 2602 is positive, during a test 2603, it determineswhether or not access to the external line is effected by a mobilestation. When the result of test 2603 is positive, test 2602 isreiterated. When the result of test 2603 is negative, during anoperation 2604, the controller 306 causes the operating mode to switchinto mobile station mode. Then, during a test 2605, the controller 306determines whether or not the external line is busy, using the linecontroller 313. When the result of test 2605 is negative, it isreiterated. When the result of test 2605 is positive, during anoperation 2606, the operating mode is switched into base station mode.

The procedure followed by the base station for requesting a new basestation when its communication quality is too low, is illustrated inFIG. 27.

The station under consideration operating in base station mode,operation 2301, its controller 306 performs a test 2302 during which itdetermines whether or not:

-   -   the quantity of energy NB available is less than the quantity        NB_min, or    -   the quality of the radio signal QR is less than the value        QR_min.

When the result of test 2302 is negative, during an operation 2310, thecontroller 306 waits for a time T7, and then the test 2302 isreiterated. When the result of test 2302 is positive, during anoperation 2303, the controller 306 performs a procedure of seeking a newbase station.

Following the operation 2303, during a test 2304, the controller 306determines whether or not a new base station has been found. When theresult of test 2304 is positive, during an operation 2305, the value DBis set to the value “1” and then, during an operation 2306, theoperating mode of the base station under consideration is switched intomobile station mode.

When the result of test 2304 is negative, during a test 2307, thecontroller 306 determines whether or not the quantity of availableenergy NB is less than the value NB_min.

When the result of test 2307 is positive, operation 2306 is performed.When the result of test 2307 is negative, during an operation 2309, thecentral unit waits for a time T8, and then test 2302 is reiterated.

Naturally, the procedure illustrated in FIG. 27 can be followed onlywhen no connection is active. Otherwise it is necessary to add aconnection deactivation operation, before operation 2306.

For a mobile station (see FIG. 28), when it receives a message“new-base-request” which designates it, operation 2801, its controller306 performs first of all a test 2802, during which it determineswhether or not on the one hand the quantity of energy NB available isgreater than the quantity NB_max and on the other hand, at the sametime, the quality of the radio signal QR is higher than the valueQR_max.

When the result of test 2802 is negative, during an operation 2807, thecontroller 306 sends a message “new-base-reject” to the base station,and thus ends the procedure of changing its operating mode. When theresult of test 2802 is positive, during an operation 2803, the centralunit 306 sends, to the base station, a message “new-base-accept”.

Following operation 2803, the controller 306 determines, during a test2804, whether or not it has received the information necessary for itsfunctioning in base station mode.

When the result of test 2804 is negative, it is reiterated. When theresult of test 2804 is positive, during an operation 2805, thecontroller 306 of the mobile station under consideration sends anacknowledgement message “ack” to the initial base station. Then, duringan operation 2806, the controller 306 switches into base stationoperating mode. The procedure of switching operating mode because offailure of the initial base station is then ended.

In order to evaluate the communication quality, a first method consistsof determining a transmission error rate.

A second method is illustrated in FIG. 29. It is intended to be executedat regular time slots. First of all, during an operation 2901, thecontroller 306 of the base station effects an initialisation of thevariables which are used in the flow diagram of FIG. 29. Next, duringoperation 2902, the controller 306 causes a message“signal-strength-request” to be broadcast to all the mobile stations inthe cell.

Each mobile station then returns a message representing the power of themessage “signal-strength-request” which it has received (see in thisregard, in the DECT standard, the use of the primitive“PL_ME_SIG_STR_req”).

So that all the answers have the time to reach it, the base stationwaits for a time T9, operation 2903, before performing an operation2904, during which the variable QR is determined as being the mean ofthe values of the answers obtained during operation 2903.

FIG. 30 illustrates a procedure followed by a mobile station which haspreviously been a base station and which has recovered the capabilitiesof functioning correctly in base station mode.

This station being in mobile station operating mode, operation 3101, itscontroller 306 performs a test 3102, during which it determines whetheror not, all at the same time:

-   -   the quantity of energy NB available is greater than the quantity        NB_max,    -   the quality of the radio signal QR is higher than the value        QR_max, and    -   the value of the variable DB is equal to “1”

When the result of test 3102 is negative, the controller 306 performs anoperation 3110, during which it waits for a time T10. Then it reiteratestest 3102.

When the result of test 3102 is positive, during an operation 3103, thecontroller 306 gives the value “0” to the variable DB. Then, during anoperation 3104, the controller 306 listens out on the channel Q. Next,during a test 3105, the controller 306 determines whether itscapabilities of being a base station are better than those of the basestation currently active.

When the result of test 3105 is negative, the procedure is ended (by afailure). When the result of test 3105 is positive, during an operation3106, the controller 306 sends a message “chg-base-request” to theactive base station. During operation 3106, the mobile station underconsideration waits for a sufficient period to. enable a communicationstation according to the present invention and functioning in basestation mode to answer, before performing a test 3107.

Then, during test 3107, the controller 306 determines whether or not ithas received a message “chg-base-accept” from the active base station.When the result of test 3107 is negative, the controller 306 considersthat the request to change base station has failed and the procedure isended (on a failure). When the result of test 3107 is positive, duringoperation 3108, the controller 306 switches the operating mode into basestation mode. Then the procedure is ended (with success).

FIG. 24 shows a second functioning mode of a communication deviceaccording to the eighth aspect of the present invention. When such acommunication device has not detected any base station (in accordancewith the prior art or after having performed all the operations andtests illustrated in FIG. 4, including one of operations 411 or 415, butwithout reproducing operation 402), and it has an informationtransmission to effect, it takes the role of base station throughout thetransmission.

To this end, during an operation 2401, the station under considerationdetermines that it has an information transmission to effect. It thenreproduces operations 401 to 403 in FIG. 4, and

-   -   if a base station which provides it with a right of access is        detected, it locks onto this base station, but    -   if no base station is detected, it performs operation 2402        during which the controller 306 causes the operating mode of the        device to switch into base station mode.

Next, during an operation 2403, the device waits for a predeterminedperiod T5, whilst regularly transmitting synchronisation signals. Thisperiod is intended to leave time for the mobile station with which thedevice wishes to communicate to lock onto it. Then, during an operation2404, the device transmits an identification request to the mobilestation with which it wishes to communicate. Next, during an operation2405, it allows a predetermined period T6 to pass, which must besufficient for the mobile station called to be able to respond.

Then, during a test 2406, the device determines whether or not it hasreceived, from at least one mobile station, an answer to theidentification request. When the result of test 2406 is negative, duringan operation 2410, the controller 306 causes the functioning mode of thedevice to switch into mobile station mode. When the result of test 2406is positive, during a test 2407, the device determines whether or notthe identity of one of the mobile stations corresponds to the identityof the station with which it must communicate.

When the result of test 2407 is negative, the operation 2410 isperformed. When the result of test 2407 is positive, during an operation2408, the transmission which the device is to make is effected. Then, atthe end of the transmission, during an operation 2409, the transmissionis ended. Finally, operation 2410 is performed.

According to a first variant, all the communication requests issuingfrom the other mobile stations are refused, the base station testing theidentity of each mobile station requesting communication and acceptingonly the communications coming from the mobile station with which it hascommunicated during operation 2408 and which are intended for it.According to this first variant, the other mobile stations therefore donot then benefit from the capability of the device of changing operatingmode.

According to a second variant, if, whilst the device is acting as a basestation, a mobile station locks onto it and attempts to establish acommunication, the device behaves as a base station, until the attemptis abandoned or, if the attempt succeeds, until the end of thecommunication, or else until another base station substitutes itself forit (see FIGS. 9 to 13). To implement this second variant, after theoperation 2409 and before performing operation 2410, the controller 306of the communication station determines, during a test (not shown),whether or not a connection with it is active, and in the affirmativereiterates this test, at regular time slots. If this test determinesthat no connection is active, operation 2410 is performed.

1. A method for changing a communication station functioning in basestation mode in a communication network, the method comprising the stepsof: performing a request operation in which a first communicationstation transmits to a second communication station functioning in basestation mode a first message representing a request to change basestation; and if the first communication station receives from the secondcommunication station a second message representing an acceptance ofchange of base station and information about communication stations inthe communication network, changing the mode of the first communicationstation to base station mode.
 2. A method according to claim 1 furthercomprising a step of switching the mode of the second communicationstation to mobile station mode.
 3. A device for changing a communicationstation functioning in base station mode in a communication network, thedevice comprising: means for performing a request operation in which afirst communication station transmits to a second communication stationfunctioning in base station mode a first message representing a requestto change base station; and means for changing the functioning of thefirst communication station to base station mode if the firstcommunication station receives from the second communication station asecond message representing an acceptance of change of base station andinformation about communication stations in the communication network.4. A device according to claim 3 further comprising means for switchingthe mode of the second communication station to mobile station mode. 5.An information storage means, which can be read by a computer or amicroprocessor, storing instructions of a computer program, saidcomputer program implementing a communication method for changing acommunication station functioning in base station mode in acommunication network, the method comprising the steps of: performing arequest operation in which a first communication station transmits to asecond communication station functioning in base station mode a firstmessage representing a request to change base station; and if the firstcommunication station receives from the second communication station asecond message representing an acceptance of change of base station andinformation about communication stations in the communication network,changing the mode of the first communication station to base stationmode.
 6. A method for changing a communication station functioning inbase station mode in a communication network, the method comprising thesteps of: performing a reception operation in which a secondcommunication station functioning in base station mode receives from afirst communication station a first message representing a request tochange base station; and if the second communication station accepts thefirst message, sending from the second communication station to thefirst communication station a second message representing an acceptanceof change of base station and information about communication stationsin the communication network.
 7. A method according to claim 6 furthercomprising a step of switching the mode of the second communicationstation to mobile station mode.
 8. A method according to claim 6 furthercomprising a step of switching the mode of the first communicationstation to base station mode.
 9. A device for changing a communicationstation functioning in base station mode in a communication network, thedevice comprising: means for performing a reception operation in which asecond communication station functioning in base station mode receivesfrom a first communication station a first message representing arequest to change base station; and means for sending from the secondcommunication station to the first communication station a secondmessage representing an acceptance of change of base station andinformation about communication stations in the communication network ifthe second communication station accepts the first message.
 10. A deviceaccording to claim 9 further comprising means for switching the mode ofthe second communication station to mobile station mode.
 11. A deviceaccording to claim 9 further comprising means for switching the mode ofthe first communication station to base station mode.
 12. An informationstorage means, which can be read by a computer or a microprocessor,storing instructions of a computer program, said computer programimplementing a communication method for changing a communication stationfunctioning in base station mode in a communication network, the methodcomprising the steps of: performing a reception operation in which asecond communication station functioning in base station mode receivesfrom a first communication station a first message representing arequest to change base station; and if the second communication stationaccepts the first message, sending from the second communication stationto the first communication station a second message representing anacceptance of change of base station and information about communicationstations in the communication network.